1. Field
The present disclosure relates generally to electronics, and more specifically to transmitters and receivers.
2. Background
A radio frequency (RF) transceiver generally includes transmit circuitry and receive circuitry connected to a transducer, such as an antenna, through a switching apparatus. The switching apparatus may comprise passive and/or active circuit elements that allow the transmit circuitry to deliver a transmit signal to the antenna, and that allow the antenna to deliver a receive signal to the receive circuitry. In some implementations, this switching apparatus can be referred to as a transmit/receive (TR or TRx) switch, and can form part of what is referred to as an RF front end of the transceiver. An RF front end may comprise some or all of a power amplifier (PA) to amplify a transmit signal, a low noise amplifier (LNA) to amplify a receive signal, one or more filter structures to allow the simultaneous passage of transmit and receive signals, a TR switch, and an antenna. A typical TR switch comprises both series and shunt devices to control the passage of both transmit and receive signals.
During operation, the TR switch may create non-linear components that can interfere with the transmit signal and, to a lesser extent, with the receive signal. Other sources of non-linearities include, for example, the power amplifier (PA), the substrate on which the transceiver is fabricated, one or more filter structures, and other elements. In addition, interfering RF signals, referred to as “jammer signals” or “jammers” may also create non-linear products at the RF front end. All of these non-linear products, when occurring as a third-order function, give rise to what is referred to as third-order intermodulation distortion (IM3), which can degrade the third-order intercept point (IP3). The IP3 is a measure of non-linearity of the RF front end as it relates to third-order intermodulation products. These non-linear products can make it difficult for the RF front end to meet linearity standards and meet other performance criteria. One of the challenges of minimizing these third-order non-linear products is that they may occur in a variety of locations in the RF front end, with each different location having a signal with a different phase and amplitude.
Currently, a varactor-based linearizer is used to linearize the shunt devices in a TR switch, but is only effective when the varactor-based linearizer shares the same node as the shunt devices and when there is no phase shift between them because it relies on exact 180 degree cancelation between the TR switch and the linearizer as the linearizer does not have phase adjustment capability.
Therefore, it would be desirable to have a linearizing circuit that can be located in a variety of places in the RF front end, and that can be adjusted for a variety of phase and amplitude conditions.